In the previous art, various combinations of ionizing and dust collecting elements have been used to produce high efficiency electronic air filters. One classic example is the standard precipitator type electronic air filter in which ionizing fine wires of about 0.005 inches diameter, charged at about 7 kilovolts are placed between grounded plates to generate a corona and charge the dust particles passing therethrough. Further down the air flow path, alternating charged and grounded plates collect the charged particles of dust.
Precipitating filters, while highly efficient, produce large number of ions and generate ozone. They also consume distinct quantities of current at high voltage, thereby requiring substantial power supplies.
Another type of electronic air filter is the non-ionizing, polarized dielectric media type. This is not as efficient as the precipitator type but it is cheaper and easier to maintain. This filter uses filament pads of non-conducting, dielectric material sandwiched between charged and grounded screens which produce electrostatic fields to polarize these pads. Any particulates passing through the filter also get polarized and they are attracted and collected by the packed filaments within the pads. This type of system produces very few ions, if any at all, no ozone and consumes virtually no current. The power supply required is thus of a low power type.
Prior art patents based on the polarization principle by the present inventor are U.S. No. 4,549,887 and No. 4,828,586. The first patent describes a pair of outer hinged screens for enclosing a pair of glass fibre pads with a central grid therebetween. The central grid, made of coarse wire mesh that is on the order of 0.020 inches in diameter, is charged to around 7000 volts and the outer screens are grounded. This combination does not generate ions significantly. The spacing between the charged screens is between one and two inches, producing a steep electric field gradient. This field gradient polarizes the non-conducting glass fibres rendering them active in trapping dust particles, and more effective than non-polarized pads.
An advantage of this type of filter is that the accumulated dust is readily removed by exchanging the glass fibre pads for fresh pads.
Both of the above designs have disadvantages. The precipitator type, although it is very efficient when clean, because of the limited surface of the collecting plates, its efficiency drops as the filter loads up with dust. The filter's loading capacity, especially for the larger particles, is very low. Maintenance of the precipitator type filters is very tedious especially in industrial and commercial applications. Also they are expensive both in original investment and operating costs since they have very elaborate construction and have large high voltage power supplies that consume anywhere from 80 to 150 watts.
The polarizing filters do not have the disadvantages of the precipitator filters but they lack efficiency.
In view of the foregoing, it is the object of my present invention to provide an electronic filter which is highly efficient, easy to maintain and inexpensive.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.